1. Field of the Invention
The present invention relates to electric rotating machines of the type provided with a superconducting stator and rotor.
2. Description of the Prior Art
In this type of machine, the stator and rotor windings are placed within heat-insulated cryogenic enclosures which are separated from each other by an evacuated annular clearance space between stator and rotor in order to reduce introductions of heat to a minimum.
The maintenance of a high vacuum within the annular clearance space calls for the use of rotary seals which achieve a high standard of leak-tightness but involve considerable difficulties in actual practice.
In order to circumvent these difficulties, a known solution proposed in U.S. Pat. No. 4,239,999 consists in completing the rotary seals placed in the vicinity of the rotor bearings by a vacuum pump system formed by two concentric sets of cylindrical sleeves provided with orifices, these sleeves being fitted one inside the other and rigidly fixed in one case to the stationary portion and in the other case to the rotating portion of the motor. This arrangement permits a reduction in standards of leak-tightness imposed on the performances of rotary seals by placing these latter on the downstream side of a pump which produces a very high vacuum. However, this is achieved at the cost of a considerable increase in complexity of the structure of the machine in the vicinity of its bearings.